The present invention relates to a transmitter.
In many branches of industry, products are stored in vessels, for example in tanks or containers. Suppliers supply the product to the vessel and users obtain it from the vessel. Since industrial products can be very expensive complex inventory systems are used to account for in and out going product.
A product received from a supplier may be valued in volume (i.e. liters or gallons) when delivered and valued as a weight (i.e. kilograms or pounds) as plant inventory. The reconciliation of incoming product value and storage value can result in financial losses if not properly managed. As bulk supply chains become more collaborative, product within a given vessel may have more than one owner. Tracking product inventory accurately becomes more important. Suppliers and users do not always have the appropriate volumetric or mass flow measurement devices on site to account for usage. If platform scales are not available at the delivery site to weigh an incoming bulk liquid delivery truck, valuation of the delivered bulk liquids given by the supplier is assumed to be correct by the user. If a custody transfer station is not available at the delivery site, a valuation of the delivered bulk liquids given by the supplier is assumed to be correct by the user.
At present individual measurement devices are used to get information on inventory of products in a tank.
Pressure measurement devices mounted on a sidewall of the vessel or on a cable or rod extending into the vessel determine hydrostatic pressure exerted on the device by the product above it. Algorithms are used to convert this hydrostatic pressure into level or volume values. Level or volume values are not fully corrected for density or temperature changes. Temperature measurement devices mounted on a sidewall of the vessel or inside the vessel on a cable or rod are used to determine the temperature of the liquid. Algorithms are used to correct the level or volume information for temperature variation. This requires another opening in the tank to accomplish.
Devices mounted on a sidewall of the vessel can be subject to wider temperature differences between product and ambient temperatures. In addition externally mounted pressure sensors are subject to tank wall movements, when the tank bulges out when filled, that can introduce significant errors.
A position of a surface of the product within the vessel can be determined with top mounted electronic measuring devices using capacitance, ultrasonic, radar, laser technologies. Algorithms are used to convert the position of the liquid into inventory level or volume information. Again, these values are not fully corrected for density or temperature changes. Often an additional pressure transmitter is used to calculate mass or density corrected volume. These hybrid solutions require multiple tank openings to accomplish.
Determination of the mass or weight of a liquid in a pressurized tank may require the addition of another pressure sensing device to account for a head pressure inside the tank above the product.
Determination of the density of the product is required by some algorithms to calculate corrected volume or level. In order to determine the density an additional pressure sensing device is mounted some known distance above the hydrostatic pressure measurement device. Density is then determined based on the distance between the two devices and the difference in pressure at their respective locations.
Another method to determine product inventory within a tank is to use mechanical floats or displacers mounted on a cable or rod inside the tank. The position of these floats is used to determine the level of the liquid. Magnetostrictive, resistance or cable tension sensing technologies are used to determine the position of the float. An additional displacer may be used to detect the density of the liquid at some point below the level measurement. Mechanical floats and displacers often require significant maintenance and are subject to material buildup errors. They often require physical entry into a tank to repair.
Load cell and strain gauge sensors are used to determine the weight of product in a tank. It is not always possible to install such sensors due to technical limitations and high installation cost.
More recently time of flight radar techniques have been used to determine the position of the surface of a product in a tank. Corresponding level measurement devices comprise a conductive probe that extends into the vessel. Microwave energy pulses are transmitted via a coupling, for example a launch plate down the probe. Some energy is reflected by the surface and returned back up the probe. A transit time from launch pulse launch to return can be used to calculate the position of the product surface.
Current practice is to use current loops to convey each individual measurement value from each measurement device to a programmable logical controller (PLC), a distributed control system (DCS) or other calculation device to perform the algorithms required to scale, compensate and correct the inventory information. Each measurement transmitter, its installation and wiring, adds cost.
If wireless technology is employed continuous power consumption from each transmitter can be over 0.5 watts.
Often process control measurement transmitters are employed in inventory measurement applications. The update times for each transmitter often exceed one second increasing power consumption for each device used. Inventory applications generally need to provide periodic, timed or event based information.
In the petroleum industry additional requirements need to be fulfilled. The American Petroleum Institute (API) defines the practice of measuring petroleum products in terms of corrected volume. The liquid position and liquid temperature at one or more points is used to calculate the inventory volume at a reference temperature using well known algorithms. Direct mass or weight measurement approaches are not generally used. There is increasing interest in using mass and/or weight determined values of petroleum products however, the current practices do not broadly support development of this information.
Floats and displacer gauging systems use mechanically moving components and sensors to measure level, temperature and density of products.
Radar gauges often combined with externally mounted temperature sensors are used to determine corrected level and volume.
Hydrostatic tank gauging systems use up to three externally mounted pressure transmitters, a temperature transmitter and a calculation box to calculate mass and sometimes density.
Hybrid systems use a top mounted radar gauge to determine level and externally mounted temperature transmitters and sometimes externally mounted pressure transmitters. A calculation box is installed to calculate mass, corrected volume and sometimes density.
Various digital buses generally of a proprietary design are used to convey the level, temperature and sometimes pressure information to the calculation box for volume correction and then to an inventory reporting and/or management system. Various types of converter boxes are used to transform one digital protocol into another at some significant expense when replacement of measurement technologies and/or suppliers are integrated into existing installations.
It is an object of the invention to provide a transmitter for providing inventory or inventory transfer information on industrial sites.
To this end the invention comprises a sensor apparatus for measurement of mass, weight, volume, level and/or density of a product in a vessel comprising:                a level sensor, comprising:                    a conductive probe extending into the vessel,            means for generating and sending short electromagnetic pulses down the probe,            means for reception of echoes of the pulses reflected at a surface of the product,            means for determining a time of flight needed for a pulse to travel down the probe and its echo to return,                        a pressure sensor,                    mounted on the probe, and                        a signal processing unit for determining mass, weight, volume, level and/or density based on measurement signals supplied by the level sensor and the pressure sensor.        
According to a preferred embodiment, the transmitter comprises at least one temperature sensor, integrated in the probe.
According to a preferred embodiment, the transmitter comprises a communication interface for reception and/or delivery of information to a user, a supplier and/or a control unit.
According to a preferred embodiment, the transmitter comprises a totalizer, for totalizing supplies or withdrawals of the product.
According to a preferred embodiment, the transmitter comprises a monitor, for monitoring unauthorized supply or withdrawal of product and leakage.
According to a preferred embodiment, the transmitter comprises a device for determining a physical position of the transmitter.
According to a preferred embodiment, the transmitter comprises an integral server for supporting communication with at least one Information Technology Network.
According to a preferred embodiment, the transmitter comprises a power supply to provide energy for the level sensor, the pressure sensor, the temperature sensors, the means, and the signal processing unit.
According to a preferred embodiment, the transmitter comprises at least one optical fibre as temperature sensor, which is integrated in the probe.
According to a preferred embodiment, the transmitter comprises at least one optically analysing pressure sensor.
The transmitter according to the invention provides multiple inventory information variables from one measurement device. Compensation and correction of any of these output values can be performed by the transmitter itself. The need for external programmable logical controllers (PLC), distributed control systems (DCS) or other calculation boxes to provide correct inventory information is eliminated. Pressure and temperature sensors are incorporated on the same probe used for time domain reflectometry.
The sensors are mounted internal to the vessel so they will generally be at the same temperature as the product.
The transmitter is able to provide level, weight, volume and/or density inventory information over time to inventory logistics operations that use this information to determine if a product delivery is required or that there is room to receive a delivery. The transmitter can simultaneously provide the information to both suppliers and users.
The invention and its advantages are explained in more detail using the figures of the drawing, in which one exemplary embodiment is shown. The same reference numerals refer to the same elements throughout the figures.